SPATIAL ASSESSMENT OF RIPARIAN BUFFERING OF UPSLOPE RUNOFF

We present an approach for analyzing landscape organization and mapping riparian zones based on gridded digital elevation data. Local contributing area entering creeks varies along the stream network. Separating local contributing area into hillslope area and riparian area allows for computation of the spatial variation of riparian buffering capacity along stream networks. We applied our techniques to the 280-ha Maimai research area in New Zealand. We found that 85% of the catchment area contributed to streams with a local catchment area of less than 20 ha, whereas only 28% of the riparian area was found along these small streams. Terrain analysis shows that upland runoff flows through the near-stream riparian zone on its way to the channel. The potential of riparian zones to buffer hillslope runoff depends partially on the size of the riparian zone relative to the adjacent hillslope or upland area. Our approach enables calculation of a spatially distributed measure of riparian to hillslope area ratios. At the 280 ha Maimai research area, we found that the ratio between riparian and hillslope area was 0.14. When we calculated this ‘buffer-capacity’ for each 20m stream reach along the stream network, the values were below 0.14 for 75% of the stream length and below 0.06 for 50% of the stream length. The proposed method provides a framework for scaling from plot scale riparian process observations to the landscape level and for comparing and classifying watersheds.